Construction, forestry and agricultural equipment and mobile working machines have movable members which are operated by an actuator, such as a motor or a hydraulic cylinder with a moving piston rod. The movable members are e.g. boom parts rotatably connected to each other in a boom crane. The boom cranes are used for handling loads or controlling a tool connected to an end of a boom part of the boom crane. Pressurized hydraulic fluid from a pump to the actuator can be controlled by a set of valves. When an operator desires to move a movable member, a control lever is operated to send signals to the valves for the cylinder associated with that movable member. The valve is opened to supply pressurized fluid to a chamber of the cylinder on one side of the piston and to allow fluid forced from the opposite chamber of the cylinder to drain to a reservoir or a tank. By varying the degree to which the valve is opened, the rate of flow into the actuator or the associated chamber can be varied, thereby moving the piston rod and the movable member at different speeds.
Hydraulic systems waste hydraulic energy (i.e. potential energy) by lowering loads using pressurized fluid, valves generating pressure losses and pumps generating hydraulic energy and fluid flow while lowering the loads. However, potential energy produced in an actuator of a hydraulic system by the loads may be used to operate another simultaneous actuator function.